This invention relates generally to rotary machines and more particularly, to methods and apparatus for operating gas turbine engines.
At least some known gas turbine engines combust a fuel and air mixture to release heat energy from the mixture to form a high temperature combustion gas stream that is channeled to a turbine via a hot gas path. The turbine converts thermal energy from the combustion gas stream to mechanical energy that rotates a turbine shaft. The output of the turbine may be used to power a machine, such as, for example, an electric generator or a pump.
At least one by-product of the combustion reaction may be subject to regulatory limitations. For example, within thermally-driven reactions, nitrogen oxide (NOx) may be formed by reactions between nitrogen and oxygen in the air initiated by the high temperatures during the combustion process. Moreover, carbon monoxide (CO) may be formed by reactions between carbon and oxygen in the air and fuel. Generally, engine efficiency increases as the temperature of the combustion gas stream entering a turbine section of the engine increases. Such increases in efficiency facilitate mitigating CO formation. However, increasing the combustion gas temperature may undesirably increase the formation of NOx.
To control NOx emissions during turbine engine operation, at least some known gas turbine engines use combustors that operate with a lean fuel/air ratio and with fuel that is premixed with air prior to being supplied into the combustor. Premixing may facilitate reducing combustion temperatures and subsequently reducing NOx formation. However, there may be limiting parameters associated with decreasing combustion temperatures, such as, for example, CO formation and lean blow-out.